Microwave noise source



June 21, 1960 H. c. POULTER 2,942,204

' MICROWAVE NOISE SOURCE Filed March 6, 1958 3 INVENTOR.

H. C. POULTER ATTORNEY making'such noise sources.

2,942,204] I MICROWAVE NOISE SOURCE U t e Sees P ren Howard CharlesPoulter, Palo AIto CaIiL, assignor to Hewlett-Packard Company,Palo'Alto; Califi, a corporation of California r Filed Mar. 6, 1958,Ser. Nit-719,640

3 Claims. (Cl. 2331-78) This invention relates to broad band microwavenoise I sources.

angle with the longitudinal axis on the waveguide. One

practical drawback of thisdevice is that unless the gaseous dischargetube is centered, within very close tlerances, with respect to thelongitudinal axis of the waveguide, the presence of the tube in thewaveguide introduces large impedance mismatches when the tube is in' itsunfired condition. These large mismatches occur over narrow-frequencybands. Very close centering of the tube, however, does not turn out tobe a practical way of The elongated gas tubes commerciallyavailable areseldom exactly straight, and break easily when a very small clearance isprovided between the glass envelope of the tube and the walls of theshield.

It is an object of the present invention to provide a broad-bandmicrowave noise source of the type described above which does notintroduce these large mismatches,

when the gas tube is in its unfired condition, and which is easier andcheaper to manufacture as it does not require close centeringtolerances.

In accordance with the'illustr'ated embodiment of this e 2 j 23. Pipesections 21 and 23 are joined or welded to the waveguide 13 and extendfrom the apertures 25 and 27 through' which the tube 11 passes throughwaveguide walls 29 and 31 respectively. Gaseous discharge through thetube 11 may be initiated byme'ans of conventional circuit shown in thedrawing and comprising voltage sources 33, coil 35, ballast resistance37 and switches 39 and 41.

In accordance with the illustrated embodiment of this invention thelarge impedance mismatches which are caused by the presence, in thewaveguide 13, of the tube 11 in its unfired condition, are avoided bycutting slots 43 and 45 in the cavity defined by the waveguide 13 andthe hollow pipe sections 21 and 23. The slots, which are preferably twoin number, should be located between the planes 47 and 49. Planes 47 and49 are planes perpendicular to the longitudinal axis of the waveguide 13within which the gas discharge tube 11 is positioned inside "thewaveguide 13. The slots 43 and 45 are narrow, and centered with respectto a plane common to the longitudinal axis of the waveguide 13 and ofthe tube 11, and positioned at least in part in the hollow pipe sections21 and 23. The slots 43 and 45 are preferablyloaded with lossy material51 such as powdered iron held together by a binder, and may be coveredon the outside by conducting shields 53 and 55 to prevent leakage fromthe waveguide 13.

The microwave noise source in accordance with the present invention doesnot introduce these large narrowband mismatches when the gas tube 11 isin its unfired condition. Its use yields more accurate noise figuremeasurements than noise sources of the prior art.

I claim: 7

l. A microwave noise generator comprising a hollow waveguide, anelongated gas discharge tube inserted within said waveguide and havingits longitudinal axis inclined at an angle with respect to thelongitudinal axis of said waveguide and extending outside of saidwaveguide, an electrode near each end of said discharge tube forproducing a discharge therein, hollow pipe sections for shielding theoutside portions of said discharge tube, said yhollow pipe sectionsbeing joined to said waveguide invention this object is accomplished byproviding the walls of the cavity defined by the waveguide andthe hollowpipes sections with at least one longitudinal slot located where the gasdischarge tube is within the waveguide, this slot being preferablyloaded with lossy material.

Other and incidental objects of this invention will be apparent to thoseskilled in the art from a reading of the following specification and aninspection of the accompanyingdrawing in which:

around two apertures therein, and at least one longitudinal slot in thewalls of the cavity defined by said waveguide and said hollow pipesections, said slot being located between the planes perpendicular tothe longitu dinal axis of the waveguide within which the gas dischargetube is inside the Waveguide and centered with Figure 1 is alongitudinal cross-sectional view of an' charge tube 11 is insertedthrough a rectangular wave-.

guide 13. The waveguide 13 is dimensioned to propagate over a prescribedfrequency range onlythe dominant mode. The tube 11 may be similar to aconventional fluorescent lamp, with the fluorescent wall coatingomitted. Thus the tube 11 has a glass envelope 15 and 1 two electrodes17 and 19 near each end of the tube 11 for producing the dischargethrough the tube. The longitudinal axis of the tube 11 is inclined at anangle of approximately nine degrees with respect to the longitudinalaxis of the waveguide 13. The portions of the tube 11 which arepositioned outside the waveguide 13 are shielded by means of two hollowpipe sections 21 and.

respect to a plane common to the longitudinal axes of the waveguide andof the gaseous discharge device, and positioned at least in part in saidhollow pipe section, and lossy material positioned in said slot to loadthe same.

2. A microwave noise generator comprising a hollow waveguide, anelongated gas discharge tube inserted within said waveguide and havingits longitudinal axis inclined at an angle with respect to thelongitudinal axis of said waveguide and extending outside of saidwaveguide, an electrode near each end of said discharge tube forproducing a discharge therein, hollow pipe sections for shielding theoutside portions of said discharge tube, said hollow pipe sections beingjoined to said waveguide around two apertures therein, and at least onelongitudinal slot in the walls of the cavity defined by said waveguideand said hollow pipe sections, said slot being located between theplanes perpendicular to the longitudinal axis of the waveguide withinwhich the gas discharge tube is inside the waveguide and centered withrespect to a plane common to the longitudinal axes of the waveguide andof the gaseous discharge device, and lossy material to load said slot.

3. A microwave noise generator comprising a hollow waveguide, anelongated gas discharge tube inserted within said waveguide and havingits longitudinal axis in said hollow pipe sections, said slots beinglocated between 10 the planes perpendicular to the longitudinal axis ofthe waveguide within which thegas discharge tube is inside thewaveguide, centered with respect to a plane common to the longitudinalaxes of the waveguide, and of the gaseous discharge device, andpositioned at least in part in said hollow pipe sections, and lossymaterial positioned in said slots to load the same.

References Cited in the file of this patent UNITED STAT ES PATENTS2,485,030 7 Bradley 061. 18, 1949 2,71 ,192 Johnson Aug. 23, 19552,766,431-. Barker Oct. 9, 1956 FOREIGN PATENTS" 1 760,386 a GreatBritain OCL 31, 1956

